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Ms Shann said the Papua New Guinea national has not been able to provide an understandable motive for why he targeted a woman whose name he didn't know.

"What in the background circumstances of a young man aged 21 ... could have led him to kill the much-loved mother? The answer to that is complex," she said.

During his childhood, Baea's violent father had affairs and his mother abandoned him when he was 14 along with his younger sister in Port Moresby, where they were living at the time.

Then Baea's father left for a new partner, with whom he had more children.

Jefford Baea said in a statement Baea was "really effected" by this and said he wanted to hurt himself.

"I believe he got jealous of happy families," Mr Baea said.

Baea had come to Australia to distract himself after passing an exam to gain entry to medical school in Turkey but his father reneged on a promise to pay for his tuition, the Victorian Supreme Court heard on Wednesday.

He inflicted 38 sharp force injuries on Ms Somawansa three days before he was due to return home.

Priyantha Hewage heard the last moments of his wife of 22 years on the phone, the court heard.

He received a call from her phone at 8.52pm but all he heard was her shouting "you go out" three times, followed by "Dos, Dos, Dos", which was her name for him, the court heard.

Panicked, Mr Hewage called for assistance from a friend who found the door to the family home hanging open and Ms Somawansa face down on the floor surrounded by blood.

Mr Hewage told police he did not know why anybody would want to hurt his wife who was a clean-living woman who loved and cared for her family.

"I love my wife very much and have had a very long and happy marriage with her," Mr Hewage said.